**2.1 Multibeam echosounder**

*Earth Crust*

**Figure 1.**

*Hypsometric profile of the ocean.*

topographical and geomorphological information effectively, and how to obtain ocean topographical information map have become important issues in the current development of marine resources and marine space utilization [2]. In particular, marine topographical information is of immense value in marine space utilization. Topography involves the recording of terrain, the three-dimensional quality of the surface, and the identification of specific landforms. It is often considered to include the graphic representation of the landform on a map by a variety of techniques, including contour lines, hypsometric tints, and relief shading [3]. Geomorphology is the branch of science that studies the characteristics and configuration and evolution of rocks and landforms [4]. In the ocean, seafloor topography is measured by multibeam echosounder (MBE), and seafloor geomorphology is

Deep sea topographical exploration mainly includes full sea depth topographical detection and near-seafloor micro-topographical detection. The advantage of full sea depth topographical is large spatial range and rapid data acquisition, and the disadvantage is limited accuracy. In contrast, near-seafloor micro-topographical exploration provides accurate detection of the seafloor using MBE, SSS, and bathymetric side-scan sonar (BSSS) carried on-board various underwater vehicles, including deep tow (DT) [5], autonomous underwater vehicle (AUV) [6], remotely operated vehicle (ROV) [7], and human occupied vehicle (HOV) [8–10]. It can obtain more accurate micro-topography and micro-geomorphology of the seafloor

In this chapter, the basic principles of three types of near-seafloor micro-topographical mapping sonars are analyzed. Then, four types of underwater vehicles suitable for near-seafloor micro-topographical mapping are briefly discussed. Next, factors affecting mapping and detection results are presented using the Jiaolong HOV and its BSSS as an example. Finally, the entire data processing and mapping methods are presented.

Three types of seafloor mapping sonars, which can be mounted of deep sea vehicles, are the multibeam echosounder (MBE), and the side-scan sonar (SSS) and

measured by side-scan sonar (SSS).

compared to full sea depth topographical detection.

the bathymetric side-scan sonar (BSSS).

**2. Near-seafloor micro-topographical mapping sonars**

**32**

An MBE works by transmitting a wide-sector-covered sound wave to the seafloor using a transmitting transducer array, and the narrow-beam receives the sound wave using a receiving transducer array. The footprints of the seafloor topography are formed by the orthogonality of the transmission and reception sectors, and these footprints are properly processed. A ping can indicate the water depth values of hundreds or even more seafloor measured points in the vertical plane perpendicular to the heading. Therefore, it is possible to accurately and quickly measure the size, shape, and height variation of underwater targets within a certain width of the route, and to reliably depict the three-dimensional features of the seafloor topography. The basic principle of an MBE is shown in **Figure 2**.

The beamforming method of MBE can be divided into two types: beam steering method (measuring the round-trip time of the reflected signal at a specific angle) and coherent method (measuring the angle of the reflected echo signal at a specific time). There are two main variables to be measured in an MBE, namely the slant distance or the distance from the acoustic transducer to each point on the seafloor and the angle from the transducer to the bottom of the ocean. All MBEs use one or both beamforming methods to determine these variables. At present, MBE manufacturers using beam steering method include Reson, Kongsberg, ATLAS, L3, and R2Sonic, whereas manufacturers using coherent method include Teledyne Benthos and Geoacoustics.

For large-area exploration of seafloor topography, shipborne deep-water MBE can be used to obtain relatively accurate seafloor topographical data. The frequency of deep-water MBE is generally approximately 12 kHz. A typical beam width is 1°× 1°, and the corresponding beam footprint is 1.75% water depth. For example, when the water depth is 5000 m, the beam footprint is approximately 87.5 m. It can be observed that the shipborne deep-water MBE cannot obtain high-precision seafloor topographical data.

Underwater vehicles, such as DT, AUV, ROV, and HOV, can carry more highfrequency MBE to near-seafloor to achieve accurate topographical detection. The corresponding MBE is designed with a special pressure-resistant design with a pressure depth of up to 6000 m or even deeper. At present, some commercial

**Figure 2.** *Basic principle of MBE.*

MBEs used for deep sea underwater vehicles are Kongsberg EM2040, Reson SeaBat 7125/T20-S, and R2Sonic 2022/4/6. They are widely used on different underwater vehicles around the world. They are widely used on different underwater vehicles around the world. Comparison of typical high-resolution MBEs for deep sea underwater vehicles is shown in **Table 1**.

## **2.2 Side-scan sonar**

SSS generates an acoustic image by emitting an acoustic signal and receiving an echo signal reflected by the seafloor to reveal sea bottom conditions, including the position, current status, height, and shape of the target. SSS has advantages of intuitive image, high resolution, and large coverage compared to other seafloor detection technologies.

SSS can be divided into two types according to the installation position of the acoustic transducer array: shipborne type and towed type. A shipborne acoustic transducer array is mounted on both sides of the ship hull. This type of SSS operates at a generally lower frequency (below 10 kHz) and has a wider swath. On the other hand, a towed acoustic transducer array is installed in the tow body, only a few tens of meters away from the seafloor, and the speed is low. The obtained side-scan image quality is higher, and even a pipeline of 10 cm and a small volume of oil drum can be distinguished. Recently, the speeds of some deep tow type SSS systems have increased, and high-resolution side-scan images can still be obtained at 10 kn.

SSS technology has two development directions: one direction is to develop BSSS technology that can obtain the topography of the seafloor while obtaining the seafloor geomorphology and the other direction is the development of synthetic aperture sonar technology with lateral resolution theoretically equal to half the physical length of the sonar array and does not increase with increasing distance.

At present, commercial SSSs for deep-sea underwater vehicles commonly used are Klein 3000, EdgeTech 2200-M, and Kongsberg dual-frequency sonar. A comparison of typical SSSs for deep sea underwater vehicles is shown in **Table 2**.

## **2.3 Bathymetric side-scan sonar**

In order to incorporate the advantage of MBE and SSS, the Institute of Acoustics of the Chinese Academy of Sciences (IOACAS) [11] developed BSSS. BSSS can detect seafloor geomorphology and topography simultaneous. The arrival angle


**35**

**Table 3.**

**Figure 3.**

*Basic principle of BSSS.*

*Advanced Mapping of the Seafloor Using Sea Vehicle Mounted Sounding Technologies*

especially suitable for installation on DT, AUV, ROV, and HOV.

Frequency 100/500 kHz 75/410 kHz

0.2° (500 kHz)

150 m (500 kHz)

and the water depth of seafloor echoes can be measured by receiving arrays of BSSS. The advantage of BSSS is high resolution, small array, and low power.

Beam tilt 5/10/15/20/25° 20° 10° ± 1°

Depth rating 3000 m 6000 m 2000 m

**IOACAS HRBSSS Teledyne,** 

Frequency 150 kHz 200 kHz 125–500 kHz Bathymetry coverage 2 × 300 m 10–12 × depth 100 m Side-scan coverage 2 × 400 m 2 × 300 m 200 m Speed 2.5 kn 3–5 kn 3 kn Depth rating 7000 m 6000 m 4000 m

**Benthos C3D**

The BSSS system's small size, lightweight, and low power consumption make it

**Klein, 3000 EdgeTech, 2200-M Kongsberg, dual-frequency** 

120/410 kHz 75/120 kHz 300/600 kHz

0.6° (120 kHz) 0.3° (410 kHz)

500 m (120 kHz) 150 m (410 kHz) **sonar**

114/410 kHz

1.0° (114 kHz) 0.3° (410 kHz)

600 m (114 kHz) 150 m (410 kHz)

> **Kongsberg, GeoSwath Plus**

*DOI: http://dx.doi.org/10.5772/intechopen.83448*

**Figure 3** shows the basic principles of BSSS.

Horizontal beams 0.7° (100 kHz)

Range 600 m (100 kHz)

*Comparison of typical SSSs for deep sea underwater vehicles.*

*Comparison of typical BSSSs for deep sea underwater vehicles.*

**Table 2.**

### **Table 1.**

*Comparison of typical high-resolution MBEs for deep sea underwater vehicles.*

*Advanced Mapping of the Seafloor Using Sea Vehicle Mounted Sounding Technologies DOI: http://dx.doi.org/10.5772/intechopen.83448*

and the water depth of seafloor echoes can be measured by receiving arrays of BSSS. The advantage of BSSS is high resolution, small array, and low power. **Figure 3** shows the basic principles of BSSS.

The BSSS system's small size, lightweight, and low power consumption make it especially suitable for installation on DT, AUV, ROV, and HOV.


#### **Table 2.**

*Earth Crust*

water vehicles is shown in **Table 1**.

**2.3 Bathymetric side-scan sonar**

**2.2 Side-scan sonar**

detection technologies.

MBEs used for deep sea underwater vehicles are Kongsberg EM2040, Reson SeaBat 7125/T20-S, and R2Sonic 2022/4/6. They are widely used on different underwater vehicles around the world. They are widely used on different underwater vehicles around the world. Comparison of typical high-resolution MBEs for deep sea under-

SSS generates an acoustic image by emitting an acoustic signal and receiving an echo signal reflected by the seafloor to reveal sea bottom conditions, including the position, current status, height, and shape of the target. SSS has advantages of intuitive image, high resolution, and large coverage compared to other seafloor

SSS can be divided into two types according to the installation position of the acoustic transducer array: shipborne type and towed type. A shipborne acoustic transducer array is mounted on both sides of the ship hull. This type of SSS operates at a generally lower frequency (below 10 kHz) and has a wider swath. On the other hand, a towed acoustic transducer array is installed in the tow body, only a few tens of meters away from the seafloor, and the speed is low. The obtained side-scan image quality is higher, and even a pipeline of 10 cm and a small volume of oil drum can be distinguished. Recently, the speeds of some deep tow type SSS systems have increased, and high-resolution side-scan images can still be obtained at 10 kn. SSS technology has two development directions: one direction is to develop BSSS technology that can obtain the topography of the seafloor while obtaining the seafloor geomorphology and the other direction is the development of synthetic aperture sonar technology with lateral resolution theoretically equal to half the physical length of the sonar array and does not increase with increasing distance. At present, commercial SSSs for deep-sea underwater vehicles commonly used are Klein 3000, EdgeTech 2200-M, and Kongsberg dual-frequency sonar. A comparison of typical SSSs for deep sea underwater vehicles is shown in **Table 2**.

In order to incorporate the advantage of MBE and SSS, the Institute of Acoustics

Frequency 200 kHz 400 kHz 200 kHz 400 kHz 200 kHz 450 kHz Transmit beamwidth 0.7° 0.4° 2.0° 1.0° 1.0° 0.45° Receive beamwidth 1.5° 0.7° 1.0° 0.5° 2.0° 0.9° Depth 635 m 315 m 450 m 175 m 400 m — Coverage 200° 200° 165° 165° 160° 160° Number of beams 400 400 256 512 1024 1024 Ping rate 60 Hz 50 Hz 50 Hz 60 Hz 60 Hz Range resolution 14.2 mm 10.5 mm 6 mm 6 mm — 10.2 mm System depth rating 6000 m 6000 m 6000 m

**Kongsberg, EM2040 Reson, SeaBat 7125 R2Sonic, Sonic 2024**

of the Chinese Academy of Sciences (IOACAS) [11] developed BSSS. BSSS can detect seafloor geomorphology and topography simultaneous. The arrival angle

*Comparison of typical high-resolution MBEs for deep sea underwater vehicles.*

**34**

**Table 1.**

*Comparison of typical SSSs for deep sea underwater vehicles.*

#### **Figure 3.**

*Basic principle of BSSS.*


#### **Table 3.**

*Comparison of typical BSSSs for deep sea underwater vehicles.*

At present, commercial BSSS for deep-sea underwater vehicles mainly includes IOACAS HRBSSS, Teledyne Benthos C3D, and Kongsberg GeoSwath Plus. The highresolution BSSS developed by IOACAS can simultaneously obtain high-resolution seafloor topography and geomorphology, and is suitable for use in complex conditions in the deep sea. HRBSSS has been successfully applied to various deep-sea underwater vehicles such as Jiaolong HOV, DTA-6000 acoustic DT, and Qianlong I/II AUV. A comparison of typical BSSSs for deep sea underwater vehicles is shown in **Table 3**.
